Body Composition

The purpose of body composition assessment is to determine an athlete's distribution of fat-free mass and fat mass. A high ratio of fat-free mass to fat mass is typically synonymous with a high strength-to-weight ratio, which is typically associated with athletic success. However, there is no single ideal body composition for all athletes in all sports. Each sport has a range of lean mass and fat mass associated with it, and each athlete in a sport has an individual range that is ideal for him or her. Athletes trying to achieve an arbitrary body composition that is not right for them are likely to place themselves at health risk and will not achieve the performance benefits they seek. In fact, athletes nearly always perform less well when they try to achieve a weight or body composition that is inconsistent with their history and genetic makeup. Therefore, the key to body composition assessment is the establishment of an acceptable range of fat-free mass and fat mass for the individual athlete. It is important to regularly monitor the fat-free mass and fat mass to ensure the stability or growth of the fat-free mass and a proportional maintenance or reduction of the fat mass. Just as much attention should be given to changes in fat-free mass (both in weight of lean mass and proportion of lean mass) as the attention traditionally given to body fat percentage.

The "fat mass and fat-free mass" model of body composition assumes that the combined weight of fat mass and fat-free mass equals total body weight. The assessment of body composition typically results in the prediction of body fat percentage, or the proportion of total weight that is composed of fat. As an example, assuming an athlete weighs 150 pounds (68 kilograms) and has a body fat percentage of 20 percent, the athlete has 30 pounds (150×.20 = 30) (13.6 kilograms) of fat weight and 120 pounds (54.4 kilograms) of fat-free weight. If this same athlete were to experience a reduction in body fat percentage to 15 percent while maintaining weight, this translates into 22.5 pounds (150×.15 = 22.5) (10.2 kilograms) of fat weight and 127.5 pounds (57.8 kilograms) of fat-free weight. This increase of 7.5 pounds(3.4 kilo grams) in fat-free weight and reduction in fat weight means the athlete is now smaller (pound for pound, lean mass takes up less space than fat mass because it has a higher density), which means he or she should be able to move more quickly and more efficiently (less drag) than before, despite being the same weight. However, if this 150-pound athlete were to maintain weight but increase fat mass while reducing lean mass, potential speed and efficiency of movement would be reduced. Weight, in the absence of knowledge of its components, is a poor measure for predicting athletic success and should not be used by itself for this purpose.

Body Composition and Performance